Its value would still increase or decrease because we are still basing our pricing in fiat but when time will come that we would not need to convert to cryptocurrency anymore then the value would be stable because we will all be using bitcoin then if that time will come. As for OPs case, his credit card charge for a transaction the he is not aware of that's why he can say that if it would be bitcoin then it would not have happen. Unfortunately, we cannot just easily shift to bitcoin because many are still against it which would include banks.
Yes, that would be the case for now. We are still waiting for the big companies to accept bitcoin as form of payment. It would happen someday when they would figure out how to not have any loss due to the fluctuating prices of cryptocurrencies which may become their disadvantage when they accept it as payment.